The polyester carbonates and methods for their preparation are described in U.S. Pat. No. 3,030,331; U.S. Pat. No. 3,169,121 and U.S. Pat. No. 3,207,814, all of which are hereby incorporated by reference. In copending application Ser. No. 755,352, a method is disclosed for the preparation of polyester carbonates by an interfacial polymerization process.
It has now been found that the polyester carbonates can be prepared from a mixed polyanhydride ester of a dicarboxylic acid and a halogen carbonic acid ester of a polyhydroxy compound. The use of the mixed polyanhydride permits the reaction with the dihydroxy compound to be carried out in a homogeneous or heterogeneous reaction mixture.